Photographs

Photographs can be highly complex structures. To obtain detailed information on identification, deterioration, use, and treatment, it is best to consult the readings listed for photographs.

Photographic prints and negatives can be composed of a number of layers, including a support, binder (or emulsion), and an image-forming component.

The support may be glass, metal, paper, or plastic. Photographic prints have a paper support; resin-coated (RC) prints are coated on both sides with polyethylene to facilitate processing.

The binder is an adhesive-like material that suspends and protects the image. The most common 19th-century binders are albumen (egg white) and collodion (guncotton). Gelatin is the most common 20th-century binder.

Silver is the major image material for black and white photographs, while color dyes make up modern color photographs, prevalent since the 1940s. Negatives have been made from glass, nitrate, acetate, and now polyester.

Controlling light, relative humidity, and temperature has the greatest impact in preserving photographic materials. In particular, cold storage slows the deterioration of film and color materials.

Specifications for storage enclosures outline the purity of materials required for photographic materials; suitable enclosures are those capable of passing the Photographic Activity Test (PAT). A proper environment, suitable enclosures, and conservation practices must be used to maintain collections in good condition.

Diagnostic Tests

A-D Strips (available from Image Permanence Institute; http://www.imagepermanenceinstitute.org/) provide a safe, simple method for detecting, measuring, and recording the severity of "vinegar syndrome" in acetate photographic film collections. Vinegar syndrome is a slow form of chemical deterioration that causes the film to shrink, buckle, and emit a strong vinegar odor. A-D Strips are acid-base indicator papers that change color in the presence of the acidic vapor given off by degrading film. This provides an objective way to document the extent of vinegar syndrome and helps in deciding when acetate cinema film, microfilm, or pictorial film needs to be duplicated.